In certain processes where there is a need for heat recovery, it is sometimes required to effect a heat exchange between, on the one hand, air and, on the other hand, a heated gaseous medium, in particular a dust-laden gas which is rich in carbon monoxide, in order to effect a preheating of the air. Such an air preheating process is employed, for example, in the method of producing crude iron which is described in British Patent Specification No. 1,386,452. In such heat exchange processes, especially when the heated gaseous medium contains carbon monoxide, it is important that there should be no mixing of the heated gaseous medium and the air, so as to avoid contamination of the air and/or the creation of an explosive mixture. It has therefore been proposed to pass the air and the heated gaseous medium through separate tubes disposed in spaced-apart, horizontal relationship in a chamber, the chamber containing a particulate heat exchange medium, for example sand, surrounding the tubes. Such heat exchangers have various disadvantages, among which may be mentioned the risk of clogging of the tube(s) which conduct the heated gaseous medium, especially when the latter has a high dust content, and the poor heat transfer obtained via the particulate heat transfer medium.
The present invention aims to provide a gas-to-gas heat exchanger which does not have the aforementioned disadvantages.